It is well known that many metal surfaces corrode over time when exposed to the atmosphere. Such corrosion typically results from oxidation of the exposed metal on the surface, as for example when iron rusts. Corrosion of metal surfaces is generally undesirable, as it weakens the structural integrity of the metal and degrades the appearance of the metal surface.
To prevent corrosion, coatings have been applied to metal surfaces to shield the metal surface from the atmosphere and prevent oxidation. Simplistic coatings, well known in the prior art, include paints and varnishes which are applied over the surface of the metal. While efficacious in preventing corrosion, such coatings are generally colored, and cover the surface to prevent viewing the metal surface.
One class of coatings which are clear and have been used for metal surfaces are those derived from alkali silicates. For example, alkali silicate coatings have been used for aluminum surfaces, and generally consist of a transparent or translucent glass-like layer over the surface of the metal to shield it from the atmosphere. While possessing desirable clarity properties, the prior art silicate coatings are generally unsuited for high performance corrosion protection. This is because prior art coating processes are incapable of producing a silicate coating that is free from microscopic defects. Where such defects exist on the surface of the coating, there is increased likelihood that the coating will fail, and the metal surface may become exposed to the atmosphere at the point of the defect, with resulting corrosion. Metal surfaces coated with prior art silicate coatings are therefore susceptible to xe2x80x9cpittingxe2x80x9d over time, the pits appearing at points on the surface where defects are present in the coating.
Consequently, there exists a need for silicate coatings for aluminum surfaces with few or no microscopic defects, such that the improved coating may exhibit high performance corrosion resistance.